In general, YAG laser processing machines as a machine tool is known for concentrating laser beam through lens means and emitting said beam on works thereby to carry out thereon processing such as drilling, cutting, welding and the like by utilizing high thermal energy density of said beam.
An example of conventional YAG laser processing machines is described hereinbelow referring to FIG. 1 showing the construction of essential portion of said processing machines.
As shown in FIG. 1, said conventional YAG laser processing machine has a YAG laser generator 3 mounted on a desired oscillator base 2. Said laser generator 3 has therein a YAG rod 6 mounted between a reflecting mirror 4 and an output mirror 5, and light from an excitation lamp 7 driven through a not shown electric power source excites atoms contained in said YAG rod 6, thereby to emit laser beam L through said output mirror 5. Said laser beam L emitted through said output mirror 5 passes successively through desired type of branching mirror 8 located at the right side of said output mirror 5, branching shutter 9 and concentrating lens 10 onto a laser output port 11 consisting of optical fiber connector and the like thereby to form a plurality of output branches. Laser beam L is transmitted from said laser output port 11, through an optical fiber 12, to a suitable laser output unit 14 having two lenses 13 located at suitable positions, then to be emitted onto desired workpiece 15. Main shutters 16 for safety use are located respectively between said YAG rod 6 and said reflecting mirror 4 as well as said output mirror 5. A monitor mirror 17 is located between said output mirror 5 and said branching mirrors 8, said monitor mirror 17 reflecting a portion of laser beam onto a power monitor 18 for checking the output state of laser beam emitted through said output mirror 5.
A suitable guide beam generator 19 is fixed at a suitable position on said oscillator base 2. Said guide beam generator 19 is used for adjusting of optical axis and can emit a visible guide beam G such as He--Ne laser. After being guided by two guide beam mirrors 20,20, said guide beam G is injected from the rear side surface of said reflecting mirror 4 to be transmitted to said laser output port 11.
YAG laser processing machines 1 having the above described construction are subjected to prior-operation or periodical checking for optical axis adjustment such as for example beam axis (beam path) of YAG laser generator 3 itself and the output beam axis (beam path) of laser beam L emitted from said YAG laser generator 3.
When carrying out said adjustment, a not shown cover member covering the elements mounted on said oscillator base 2 is first removed, and said main shutters 16 are opened with said YAG laser generator 3 and said guide beam generator 19 being in respective operable states. Further, at adjusting of optical axis of output beam, said guide beam G is viewed by a not shown guide beam visual inspection means such as fiber scope.
However, said YAG laser generator 3 and said guide beam generator 19 are kept in operable state during said adjustment in the conventional YAG laser processing machines 1 as described above; therefore in this structure of conventional laser processing machines, there occurs a safety problem that said YAG laser generator 3 is accidentally driven owing to an operational error of operator when carrying out said adjustment of optical axis of said output beam which does not need the operable state of said YAG laser generator 3, and said laser beam L is reflected at said concentrating lens 10 and at the end surfaces of said optical fiber 12, resulting in leakage of said laser beam L outwards from rear surface of said branching mirror 8 as shown by dashed arrow A in FIG. 1.
Further, at the adjustment of optical axis of output beam, it is necessary to visually check said guide beam G by means of a guide beam visual inspection means not shown. This adjustment operation gives rise to a large load on the eyes of operator which are most sensible to light, especially when carrying out said adjustment for a long period of time.